You get 30 TB traffic inclusive with the smallest Hetzner server that has ECC (4 core Xeon with 64GB RAM). And that is for ~70 EUR per month + setup fee.
That amount of traffic is more than 2000 EUR per month at AWS. Of course this is comparing entirely different things, but still, if you have significant traffic and can't avoid it with a CDN or something like that, AWS (as well as Google and Microsoft clouds) get seriously expensive.
That's just referring to the VPS itself. If you keep reading the FAQ you'll see that there are ways to exceed that amount.
Plus there's nothing stopping someone breaking into your account and upgrading it in all kinds of evil ways (which has been a huge hassle with AWS tokens being stolen from e.g. Github).
Not OP, but I've heard of people getting hijacked and finding a bunch of VPSs spun up sending out spam and other malware related stuff. Maybe that's what they mean.
> Data transfer overages above the free allowance are charged at $0.09/GB.
On the $5 instance the second TB (at $90) is 18 times as expensive as the instance itself with the first TB included.